Ultimately, Konner is attempting to construct a sort of theory that encompasses all of human life. The evolutionary processes he describes are the way in which at every level—the genome, the nervous system, society, and culture—we, who carry along information accumulated over billions of years, continually interact with the environment, and thereby learn and change in response to it. Children, who are shaping and organizing their very selves, experience this most powerfully. And it should not be surprising, he speculates, if children—in the midst of the most exploratory phase of human life, thanks to “their huge, fast-growing, thoroughly dynamic brains”—have throughout the history of the species often been at the vanguard of cultural innovation.

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KONNER IS ESPECIALLY interested in play, which is not unique to humans and, indeed, seems to have been present, like the mother-offspring bond, from the dawn of mammals. The smartest mammals are the most playful, so these traits have apparently evolved together. Play, Konner says, “combining as it does great energy expenditure and risk with apparent pointlessness, is a central paradox of evolutionary biology.” It seems to have multiple functions—exercise, learning, sharpening skills—and the positive emotions it invokes may be an adaptation that encourages us to try new things and learn with more flexibility. In fact, it may be the primary means nature has found to develop our brains.